Derive map units from IFC scale

Use IfcMapConversion.Scale as the source of truth for converting map coordinates to metres, instead of deriving that scale from IfcProjectedCRS.MapUnit. Bump the sidecar version because cached georef matrices and unit scales may differ under the new interpretation.

Generated with the assistance of an AI coding tool.

src/ifcviewer/tests/test_federation.cpp

@@ -18,6 +18,7 @@
  ********************************************************************************/
 
 #include "Federation.h"
+#include "Geolocation.h"
 
 #include <catch2/catch_test_macros.hpp>
 
@@ -457,6 +458,25 @@ TEST_CASE("composeFederatedFalseOrigin scales by federation unit",
     REQUIRE(std::abs(M(0, 3) - (-0.3048)) < 1e-9);
 }
 
+TEST_CASE("helmert metres transform consumes Scale through map unit scale",
+          "[federation][georef]") {
+    HelmertTransformation params;
+    params.e = 500000.0;
+    params.n = 7000000.0;
+    params.scale = 0.001;  // project mm -> map numeric metres
+
+    const double project_length_to_meters = 0.001;
+    const double map_unit_to_meters = project_length_to_meters / params.scale;
+    Eigen::Matrix4d M = helmertMetersFromParameters(params, map_unit_to_meters);
+
+    Eigen::Vector4d local_m(10.0, 20.0, 0.0, 1.0);
+    Eigen::Vector4d global_m = M * local_m;
+
+    REQUIRE(std::abs(map_unit_to_meters - 1.0) < 1e-12);
+    REQUIRE(std::abs(global_m.x() - 500010.0) < 1e-9);
+    REQUIRE(std::abs(global_m.y() - 7000020.0) < 1e-9);
+}
+
 TEST_CASE("addGroup creates a top-level group; addGroup with parent nests it",
           "[federation][groups]") {
     ensureQApp();